<template>
  <scroll class="listview"
          :data="data"
          ref="listview"
          :listenScroll = "listenScroll"
          @scroll = "scroll"
          :probeType = probeType
  >
    <ul>
      <li v-for="group in data" class="list-group" ref="listGroup">
        <h2 class="list-group-title">{{group.title}}</h2>
        <ul>
          <li v-for="item in group.items" class="list-group-item">
            <img class="avatar" v-lazy="item.avatar" alt="">
            <span class="name">{{item.name}}</span>
          </li>
        </ul>
      </li>
    </ul>
    <div class="list-shortcut" @touchstart="onShortcutTouchStart" @touchmove.stop.prevent="onShortcutTouchMove">
      <ul>
        <li v-for="(item, index) in shortcutList"
            class="item"
            :data-index="index"
            :class="{current : currentIndex === index}"
        >
          {{item}}
        </li>
      </ul>
    </div>
    <div class="list-fixed" v-show="fixedTitle" ref="fixed">
      <h1 class="fixed-title">{{fixedTitle}}</h1>
    </div>
    <div class="loading-container" v-show="!data.length">
      <loading></loading>
    </div>
  </scroll>
</template>

<script>
    import Scroll from 'base/scroll/scroll';
    import Loading from 'base/loading/loading'
    import {getData} from "common/js/dom";

    const ANCKOR_HEIGHT = 18
    const TITLE_HEIGHT = 30

    export default {
        name: "listview",
        created() {
            this.touch = {};
            this.listenScroll = true;
            this.listHeight = [];
            this.probeType = 3
        },
        data() {
          return {
            scrollY: -1,
            currentIndex: 0,
            diff: -1
          }
        },
        props: {
          data: {
            type: Array,
            default: []
          }
        },
        computed: {
          shortcutList() {
            return this.data.map((group) => {
              return group.title.substr(0, 1)
            })
          },
          fixedTitle() {
            return this.data[this.currentIndex] ? this.data[this.currentIndex].title : ''
          }
        },
        methods: {
          onShortcutTouchStart(e) {
            let anchoIndex = getData(e.target, 'index')
            let firstTouch = e.touches[0]
            this.touch.y1 = firstTouch.pageY
            this.touch.anchorIndex = anchoIndex
            this._scrollTo(anchoIndex)
          },
          onShortcutTouchMove(e) {
            let firstTouch = e.touches[0]
            this.touch.y2 = firstTouch.pageY
            let delta = (this.touch.y2 - this.touch.y1) / ANCKOR_HEIGHT | 0
            let anchorIndex = parseInt(this.touch.anchorIndex) + delta;
            this._scrollTo(anchorIndex);
          },
          scroll(pos) {
            this.scrollY = pos.y
          },
          _scrollTo(index) {
            if (!index && index !== 0) {
              return
            }
            if (index < 0) {
              index = 0
            } else if (index > this.listHeight.length - 2) {
              index = this.listHeight.length - 2
            }
            this.scrollY = -this.listHeight[index]
            this.$refs.listview.scrollToElement(this.$refs.listGroup[index], 0)
          },
          _calculateHeight() {
            this.listHeight = []
            let height = 0;
            this.listHeight.push(height);
            const list = this.$refs.listGroup;
            for (let i = 0; i < list.length; i ++) {
              let item = list[i];
              height += item.clientWidth
              this.listHeight.push(height)
            }
          }
        },
        watch: {
          data() {
            setTimeout(() => {
              this._calculateHeight()
            }, 20)
          },
          scrollY(newY) {
            const listHeight = this.listHeight;

            if (newY > 0) {
              this.currentIndex = 0
              return
            }

            for (let i = 0; i < listHeight.length - 1; i++) {
              let height1 = listHeight[i];
              let height2 = listHeight[i + 1];
              if (-newY >= height1 && -newY < height2) {
                this.currentIndex = i;
                this.diff = height2 = newY
                return
              }
            }
            this.currentIndex = listHeight.length - 2;
          },
          diff(newVal) {
            let fixedTop = (newVal>0 && newVal<TITLE_HEIGHT) ? newVal - TITLE_HEIGHT : 0;
            if (this.fixedTop === fixedTop)  {
              return
            }
            this.fixedTop = fixedTop
            this.$refs.fixed.style.transform = `translate3d(0, ${fixedTop}px, 0)`
          }
        },
        components: {
          Scroll,
          Loading
        }
    }
</script>

<style scoped lang="stylus" rel="stylesheet/stylus">
  @import '~common/stylus/variable';

  .listview
    position: relative
    width: 100%
    height: 100%
    overflow: hidden
    background: $color-background
    .list-group
      padding-bottom: 30px
      .list-group-title
        height: 30px
        line-height: 30px
        padding-left: 20px
        font-size: $font-size-small
        color: $color-text-l
        background: $color-highlight-background
      .list-group-item
        display: flex
        align-items: center
        padding: 20px 0 0 30px
        .avatar
          width: 50px
          height: 50px
          border-radius: 50%
        .name
          margin-left: 20px
          color: $color-text-l
          font-size: $font-size-medium
    .list-shortcut
      position: absolute
      z-index: 30
      right: 0
      top: 50%
      transform: translateY(-50%)
      width: 20px
      padding: 20px 0
      border-radius: 10px
      text-align: center
      background: $color-background-d
      font-family: Helvetica
      .item
        padding: 3px
        line-height: 1
        color: $color-text-l
        font-size: $font-size-small
        &.current
          color: $color-theme
    .list-fixed
      position: absolute
      top: 0
      left: 0
      width: 100%
      .fixed-title
        height: 30px
        line-height: 30px
        padding-left: 20px
        font-size: $font-size-small
        color: $color-text-l
        background: $color-highlight-background
    .loading-container
      position: absolute
      width: 100%
      top: 50%
      transform: translateY(-50%)
</style>
